In the power generation industry, various types of non-destructive tests are often used to determine if defects are present in an object. Non-destructive test methods that have been used in the past include liquid penetration, magnetic particle, eddy current, radiography, and ultrasound. These test methods tend to be time consuming and expensive to perform. In recent years, it has become more important to develop inspection techniques which optimize the efficiency of testing by reducing costs and inspection time.
One such example of a recently developed inspection method can be found in U.S. Pat. No. 6,236,049 by Thomas, et al. titled “Infrared Imaging of Ultrasonically Excited Subsurface Defects in Materials.” This patent describes the use of infrared or thermal imaging of ultrasonically excited subsurface defects in a material. A source for ultrasound is used to send sound waves to a component, while images of the component are captured with a thermal imaging camera. Vibrational energy from the sound in the material causes defects in the component to heat up and become visible in the images generated by the camera.
The Thomas '049 patent also describes the use of a coupler at the end of a transducer that is used to transfer the sound waves from the source to the component. The coupler prevents the transducer from bouncing or walking along the component. Applicants have recognized that a disadvantage of using a coupler is that a portion of the vibrational energy is transferred into the component, and a rather large amount of vibrational energy is lost. The use of the coupler makes the system less efficient.
As quality assurance becomes more important, particularly in inspection, a need exists to not only determine if a defect is present in an object under test, but to also inexpensively determine the severity of the defect.